Sestak, who won his primary in the face of President Obama's support for Specter, has taken full advantage, arguing that Toomey may be stylistically different from the colorful candidate across the river but is substantively quite similar. Toomey was president of the conservative Club for Growth, a group that targeted moderate Republicans in primaries, and Sestak says his opponent and O'Donnell want to drive middle-of-the-roaders out of the GOP.

You might also imagine, from all the times he cites it, that Sestak's favorite book is Toomey's 2009 supply-side manifesto, "The Road to Prosperity," which endorses private accounts for Social Security and a moratorium on all corporate taxes.

"Congressman Toomey is not a witch," Sestak loves to say, "but his book is very scary."

All this has allowed Sestak to close the gap with Toomey and move momentum to his side. Toomey's campaign argues that Sestak has simply brought some Democrats home and can point to some recent polling favorable to the Republican. But Toomey tacitly acknowledges the damage O'Donnell has done him because he carefully delineates his differences with her.

And the O'Donnell effect has larger implications. Republican gains next week are inevitable. But if Senate candidates on the right end of Republican politics lose here and in most of the other states they are contesting (Colorado, Wisconsin, Alaska, Kentucky and Nevada), conservatives will have trouble claiming this election as an ideological mandate and a sign that the country had moved well to the right of where it was two years ago.

So far, being righter-than-right has been anything but helpful. O'Donnell's nomination virtually sealed a victory for Democrat Chris Coons. In Colorado, Democratic Sen. Michael Bennet, after spending the summer under assault from anonymously funded conservative groups, has been closing in on Tea Party favorite Ken Buck. In Wisconsin, Sen. Russ Feingold has narrowed Republican Ron Johnson's once substantial lead.

In Alaska, the Tea Party's Joe Miller faces a formidable write-in challenge from Sen. Lisa Murkowski, whom he defeated in the Republican primary, even as Democrat Scott McAdams battles to sneak through on the GOP split.

Republican Rand Paul has clung to a lead over Democrat Jack Conway in Kentucky, a very red state where a Republican should not be having so much trouble. As for Nevada, nobody knows if Senate Majority Leader Harry Reid will prevail over marquee Tea Party candidate Sharron Angle, but Angle's bizarre brand of conservatism is the one thing giving Reid a fighting chance.